Functions of the thalamus in perception and cognition
The pulvinar is the largest nucleus in the primate thalamus and is considered a higher-order thalamic nucleus
because it forms input-output loops almost exclusively with the cortex. From an anatomical perspective, the
pulvinar is ideally positioned to regulate the transmission of information to the cortex and between cortical
areas to influence perceptual and cognitive processes. However, experimental evidence in support of such a
functional role has been sparse. The most compelling evidence for the pulvinar playing an important role in
visual perception and cognition has come from lesion studies in humans and monkeys. These studies point to
the critical involvement of the pulvinar in a number of fundamental cognitive functions, including orienting
responses and the exploration of visual space, feature binding, and the filtering of unwanted information. The
underlying neural correlates of these cognitive operations in the pulvinar are largely unclear.
One of the lab's major objectives is to define the role of the pulvinar in visual attention using an integrated
multi-modal methods approach that includes fMRI, dMRI, electrophysiology, and behavioral measures.
Attention network dynamics
The visual environment contains more information than can be processed simultaneously.
Due to this limited processing capacity of the visual system, it is necessary to select the behaviorally most
relevant information for further processing and to filter out the unwanted information, a fundamental ability
known as attentional selection. There is converging evidence from physiology studies in monkeys and neuroimaging studies
in humans that attentional selection occurs at multiple stages along the visual pathway. For example, neural responses are
modulated by spatially directed attention to a target location as early as in the thalamus and at each successive cortical
processing stage as well. These modulatory influences appear to be generated by a network of higher-order areas in frontal
and parietal cortex that includes the frontal eye fields (FEF) and the lateral intraparietal area (LIP) in the monkey and
functionally similar areas in the human. In monkeys, physiology studies have begun to characterize the interactions across
the network by simultaneously recording from two or more interconnected nodes of the attention network. One important result
of these studies suggests that the strength of attentional modulation is linked to the strength of neural synchrony between areas.
In contrast, in humans, little is known about the temporal dynamics and functional interactions across areas of the attention network. Further,
despite the macaque brain serving as the prime model for our basic understanding of human brain function, it remains unclear how neural mechanisms
related to perception and cognition compare across primate species. Another major objective in the laboratory is to characterize the temporal dynamics
of the attention network in human ECoG patients and compare electrophysiological signals related to spatial attention across primate species.
Attentional selection from natural scenes
One of the great challenges of cognitive neuroscience is to reveal the neural mechanisms underlying perceptual and cognitive
processes that are utilized under naturalistic conditions. Selecting a complex object from a cluttered environment (i.e. a natural
scene) presents a particularly complicated problem, since the exact location of the object is often unknown, and an object has an almost
infinite number of visual appearances (due, e.g., to variations in size and orientation). Despite these challenges, the visual system has an
extraordinary capability to extract categorical information (e.g. detecting people or cars) quickly and efficiently from natural scenes, yet little is known about
the neural mechanisms related to such real-world search. Recent studies from our laboratory have identified a category-specific biasing mechanism that operates
in parallel across the visual field and enhances processing of objects that belong to the task-relevant category. Characterizing this biasing mechanism during
real-world search of natural scenes is another major objective in the lab. We employ a multi-modal methods approach (i.e., psychophysics, fMRI, TMS, and ECoG
recordings) with virtually identical experimental designs across approaches and subject populations.
Neuromodulation in the attention network
Cholinergic and dopaminergic systems are widely accepted to play a functional role in selective attention, but little is known about the
specific effects that this modulation has on neural responses and on behavior. Acetylcholine (ACh) is the primary neuromodulator in the
pulvinar nucleus of the thalamus\ which is a critical node in the attention control network. For example, our recent studies have
demonstrated that the pulvinar synchronizes areas of visual cortex according to behavioral demands. We hypothesize that ACh plays
an important role in the pulvinar-mediated control of attentional responses in cortex. Our laboratory is probing the effects of cholinergic
modulation in the pulvinar on visual cortical responses linking ACh-dependent neural changes in visual cortex with behavior in an
effort to define a causal role of the pulvinar in cognitive processing.